1. Field of the Invention
This invention relates to a semiconductor integrated circuit, especially to a semiconductor integrated circuit with an electrostatic discharge protection device.
2. Description of the Related Art
An electrostatic discharge protection device has been formed in a semiconductor integrated circuit of prior arts to protect an internal circuit from electrostatic discharge. A device with a bipolar transistor, a diode, or a MOS transistor is used as an electrostatic discharge protection device. The electrostatic discharge protection device is connected to a pad that is an electrode connected to an internal circuit receiving an external input signal or an electrode receiving an output signal from the internal circuit. When excessive noise pulse is applied to the pad, the electrostatic discharge protection device turns on letting an electric current with the noise pulse go to a power source line or a ground line for protecting the internal circuit. The semiconductor integrated circuit with the electrostatic discharge protection device is disclosed in Japanese Patent Application Publication Nos. 2003-264238 and 2005-057138.
However, the dielectric strength decreases in some pattern layouts of the semiconductor integrated circuit, further inviting problems such as latch-up and malfunction of the internal circuit due to the noise pulse applied to the pad.